Hi Everyone: Been a while since my last post.
I have a simple question regarding charging a capacitor.
Basically I have a high voltage line in which I want to connect to a capacitor to charge it. Once the capacitor is charged, the high voltage line needs to be 'disconnected' from the capacitor. The capacitor then discharges into a load, and the process repeats.
My first idea was using a high voltage power mosfet. This becomes a problem in and of itself, because the mosfet requires a special gate driver to get the correct voltages. While I can get a driver that 'floats' with the high voltage switching line, resistive losses may become a problem when the device is switch on. Not to mention high voltage mosfets seem to have very high RDS on values.
My next idea is based on diode and thyristor theory. I have just become acquainted with thyristors as I never seemed to have to use them. They seem to be high power devices, perfect for this application; however, they have the nasty side effect of not being able to be turned off from the control gate signal. Basically, if you have a diode in series with a capacitor, current flows through the diode until the capacitor is charged. Then the current flow stops (if the cap doesn't have anything to discharge into). If you put a load on the cap, the cap will discharge into the load and the diode will allow the cap to be recharged.
Anyhow.. my idea is this. Instead of using a diode, I use a thyristor. The high voltage line comes from a switching power supply (say 400 volts), and if possible, I would like it to remain a DC voltage. When the thyristor gate is triggered, current flows through the thyristor to charge the cap. Once the cap is charged, the thyristor turns off, because there technically would be no current. In this way, the thyristor would do exactly what I wanted as per the problem statement. Now.. I know there is a voltage drop across the thyristor when it conducts, like a diode, therefore, I do not know if this method would work. A schematic of my idea is attached. Keep in mind, that I am just showing the components in the circuit. Any component model numbers shown are not what I would use in the end.
Basically, what happens is that the cap is charged via the thyristor when the control signal is applied. The cap charges all the way, and the thyristor shuts off disconnecting the HV supply from the system. Finally, the switch element (most likely a mosfet) discharges the cap into a load. The switch element would obviously be timed with the thyristor control signal to make this happen correctly.
So the question is: is this how it will work in reality, or will the thyristor not work as planned? Any ideas?
Thanks,
LostTime77
I have a simple question regarding charging a capacitor.
Basically I have a high voltage line in which I want to connect to a capacitor to charge it. Once the capacitor is charged, the high voltage line needs to be 'disconnected' from the capacitor. The capacitor then discharges into a load, and the process repeats.
My first idea was using a high voltage power mosfet. This becomes a problem in and of itself, because the mosfet requires a special gate driver to get the correct voltages. While I can get a driver that 'floats' with the high voltage switching line, resistive losses may become a problem when the device is switch on. Not to mention high voltage mosfets seem to have very high RDS on values.
My next idea is based on diode and thyristor theory. I have just become acquainted with thyristors as I never seemed to have to use them. They seem to be high power devices, perfect for this application; however, they have the nasty side effect of not being able to be turned off from the control gate signal. Basically, if you have a diode in series with a capacitor, current flows through the diode until the capacitor is charged. Then the current flow stops (if the cap doesn't have anything to discharge into). If you put a load on the cap, the cap will discharge into the load and the diode will allow the cap to be recharged.
Anyhow.. my idea is this. Instead of using a diode, I use a thyristor. The high voltage line comes from a switching power supply (say 400 volts), and if possible, I would like it to remain a DC voltage. When the thyristor gate is triggered, current flows through the thyristor to charge the cap. Once the cap is charged, the thyristor turns off, because there technically would be no current. In this way, the thyristor would do exactly what I wanted as per the problem statement. Now.. I know there is a voltage drop across the thyristor when it conducts, like a diode, therefore, I do not know if this method would work. A schematic of my idea is attached. Keep in mind, that I am just showing the components in the circuit. Any component model numbers shown are not what I would use in the end.
Basically, what happens is that the cap is charged via the thyristor when the control signal is applied. The cap charges all the way, and the thyristor shuts off disconnecting the HV supply from the system. Finally, the switch element (most likely a mosfet) discharges the cap into a load. The switch element would obviously be timed with the thyristor control signal to make this happen correctly.
So the question is: is this how it will work in reality, or will the thyristor not work as planned? Any ideas?
Thanks,
LostTime77
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